Requirements for the BC value in the UASB reactor
Release Date:
2026/04/23
The UASB reactor requires an influent B/C ratio of ≥0.3 to ensure that the wastewater has sufficient biodegradability to support the normal metabolism of anaerobic microorganisms and the formation of granular sludge.
According to numerous engineering practices and technical guidelines, the B/C (BOD₅/COD) ratio is a key indicator for determining whether organic wastewater is suitable for the UASB process:
When B/C ≥ 0.3, it indicates that the wastewater contains a sufficient proportion of biodegradable organic matter and is suitable for anaerobic treatment;
If B/C < 0.3, the wastewater is considered difficult to degrade or non-biodegradable, and its biodegradability must first be improved through pretreatment methods such as hydrolysis and acidification. Otherwise, it may lead to difficulties in reactor start-up, low gas production rates, and poor sludge activity.
In addition, combining these with other influent conditions can further ensure the stable operation of the UASB:
COD concentration: preferably ≥1500 mg/L;
pH: 6.0–8.0;
BOD/COD > 0.3 (or B/C > 0.3);
Ammonia nitrogen: ≤2000 mg/L;
Sulfate: ≤1000 mg/L.
Therefore, in practical applications, if the B/C ratio of the raw water is low, it is recommended to adopt a “hydrolysis-acidification + UASB” combined process to improve biodegradability before feeding the influent into the UASB reactor, thereby enhancing treatment efficiency and the system’s resistance to shock loads.
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